Bloomicy,
The whole idea around Atkins and other Low Carb plans is to keeps Carb intakes around 20-30 grams per day. The reason is to put your body into Ketosis, where it burns fat for engery rather than carbs. Now as far as cheating goes, a single meal can take you out of Ketosis, and if you really go wild and consume 7000 calories, yes you could gain two pounds. Now assuming you are human, most of us cheat every so often but usually not to this extent. A one meal deviation might keep you out of ketosis for a few hours, depending on the amount and composition of the meal, and that you get back into LC eating the next meal.
From my view the problem with cheating is that 1) it can produce a habit of cheating 2) it can bring with it guilt and self condemnation which can lead people to give up all together.
Atkins or any other LC plan is not any more unforgiving of slip ups. The real question may be why is your friend cheating in the first place? If they do cheat do they feel guilty? Why?
There are a number of type of people here on this forum ranging from those trying to lose a few pounds, to those like myself trying to make a lifestyle change and lose a few hundred pounds and keep them off.
For me this is not a "Diet". I've done "Diets" and I lose weight and then it comes back. I chose to call this a LifeStyle change because I believe my body handles food and exercise differently than other peoples. To me, there are going to be time when I am unable or chose not to fuel my body using LC foods. You can call this cheating if you like, but it's a decision that I make, that I am in control of making. My goal however, is to try and and make LC food choices when it comes to selecting foods on a consitent basis.
There are other people who lack the ability to control their food choices. These people need addition support, structure, and accountability in there lifes. Some of this we can help provide here, some we can not.
Seems to me your friend might not like the limits that LC puts on their food choices and therefore it might not be the right plan for them. One might question their commitment to the LC plan in the first place? But to say that an simple deviation from an LC plan caused a two pound gain is not very realistic or it must have been one heck of a sandwich.
Regards,
Lux